Apparatus for measuring high pressures at low temperatures are known in the prior art. For example, measurement of pressure at temperatures below 350° F. is frequently accomplished with pressure transducers that position a large diameter diaphragm such that the diaphragm is exposed to the pressure to be measured. Such diaphragms are typically thin or corrugated and have relatively large diameters. The diaphragms are often rigidly clamped or welded in place at the perimeter of the diaphragm such that the central portion of the diaphragm is compliant and deflects proportionally in response to pressure. The amount of deflection of the diaphragm may be used to calculate the pressure.
Pressure measurement techniques for relatively moderate temperatures are well known in the prior art. As the range of pressure to be measured in a family of transducers increases, it may be necessary to increase the thickness of the diaphragm to assure all of the transducers in the family deflect approximately the same amount when each transducer in the family is subjected to 100% of its pressure rating. All other factors being equal, the stress on the diaphragm increases as the thickness of the diaphragm increases or as the diameter of the diaphragm decreases. So, for a given diameter of transducer, there exists a maximum pressure rating above which the stresses in the diaphragm exceed the allowable stresses for the material, and the transducer begins to yield and deform plastically. Yielding and plastic deformation occur because the bending stresses around the circumference of the diaphragm exceeds the elastic strength of the diaphragm material. Such yielding and plastic deformation results in a loss of repeatability and stability of the transducer.
Pressure measurement at high temperatures creates additional problems due to the melting point of some materials used in conventional transducers and because the strength of most materials diminish at high temperatures. Therefore, there exists a need for novel arrangements of apparatus and novel methods for using such apparatus to measure relatively high pressures at high temperatures with small diameter transducers.